1. Field of Invention
The present invention generally relates to inductors, and more particularly to an inductor implemented using, semiconductor fabricating methods.
2. Description of Related Art
The development of telecommunication technologies is growing rapidly nowadays, thanks to considerable advancement of semiconductor technologies. Generally speaking, the manufacturing of a high-frequency inductor in a semiconductor fabrication process is very difficult. An ideal semiconductor inductor needs to possess good characteristics such as high inductance density, high quality factor, and high stability, which therefore make the inductors difficult to produce. During the manufacturing of inductors, inductance value can be increased by increasing number of turns of an inductor. Unfortunately, the parasitic capacitance on a substrate is also increased therewith, such that the self-resonant frequency is reduced. Normally, a multi-level inductor structure can be used to solve this problem, which is described hereinafter.
FIG. 1 shows a conventional multi-level inductor, which is disclosed in U.S. Pat. No. 5,610,433. As shown in this figure, inductor 10 uses coils M1, M2, and M3 to build a three-layers inductor structure, in which every coil can be made from several circular metal conductors of different diameters. The coil structure shown in FIG. 1, which has an inner conductor and an outer circular conductor, is one of the examples. The diameter of the coil is typically ranged from tens of micro meters to thousands of micro meters. Metal material used can be aluminium or other materials with a high conductivity. Interconnections between coils in every layer are also shown in this figure. This kind of interconnection can be implemented by using a via between isolating layers. As shown in the figure, where directions of current are designated by arrows, a current is fed into the inductor 10 via a conducting wire 11, and flowed out from a conducting wire 48.
Through the multi-level inductor structure can achieve the objective of increasing the inductance per unit square measurement, it complicates the manufacturing process, which subsequently reduces the reliability. Furthermore, typical microwave circuits are not based on the multi-level structure. It will be uneconomical and time-consuming, if the inductor is produced using additional metalization processes and masks.
Another conventional way to increase the inductance value is the use of additional number of turns for a coil. Unfortunately, these additional turns not only take extra space, but also reduce the inductance per unit square measurement. Usable space is therefore wasted and the self-resonant frequency is reduced. The preset objective can not be achieved by using the additional turns in a coil.
As a summary, the conventional inductor structure has the following disadvantages:
1. The multi-level inductor structure complicates the manufacturing process, such that the reliability is reduced. PA1 2. The multi-level inductor structure requires additional metalization processes and masks, which is uneconomical and time-consuming. PA1 3. Increasing number of turns for a coil not only reduces the self-resonant frequency, but also significantly reduces the inductance per unit square measurement, resulting in wastes of usable space.